Validate data in excel programmatically - new to VBA

I have external users doing data entry on an excel file.
I've used data validation where I can, but cannot use VBA on the data entry file itself because end-users are restricted from using files with macros, and also use different versions of excel, etc.

I find that users can copy/paste into a data-validated field and remove the data validation. I can fix this using VBA, but again, end-users cannot enable macros.

I created a macro that takes data from the data entry file, and places it in an 'import' excel file (in which I can use VBA). Data in the 'import' excel file will be imported into Access.

My question is, how do I validate the data in the 'import' excel file programmatically.
For example, I have a customerID that can only be 9 characters long. If somehow the end-user was able to copy/paste an ID with less than or greater than 9 characters, I want my import file to tell me in which record this has occurred.

Please help! And thanks!